This invention relates to motor control systems and, more particularly, to an arrangement for use in conjunction with such a system for indicating a motor overload condition.
When the load on a motor driven by an alternating current is mechanically varied, it can cause an overload condition which can damage the motor. Such overload condition may be an indication of a mechanical jamming of a moving element driven by the motor, which jamming can result in damage to the element driven by the motor or to the obstruction causing the jam, as well as damage to the motor itself. This is particularly relevant to motor driven doors, such as garage doors, which are subject to encountering obstructions in their path of travel while closing. It is therefore a primary object of this invention to provide an arrangement for detecting such a jamming by measuring the loading on the motor.
It is a more specific object of this invention to provide such an arrangement which is accurate and reliable independent of motor size, amperage, voltage or wattage.
It is another object of this invention to provide such an arrangement in conjunction with a door operator which is so arranged that jams are automatically released after being detected.